This invention relates to a hydraulic power unit. More specifically this disclosure relates to a hydraulic power unit that uses an electrically actuated bypass valve to redirect fluid from an outlet to an inlet.
Naturally commutated hydraulic power pumps are known in the prior art. Such pumps are also referred to as check valve hydraulic pumps or wobble plate hydraulic pumps. Adjustable displacement hydraulic power pumps have many benefits versus fixed displacement power pumps. For example, a hydraulic pump may receive mechanical energy from a mechanical power means such as an internal combustion engine, turbine, electric motor or the like. Hydraulic power pumps typically convert rotational mechanical energy to hydraulic fluid power that is used to actuate a hydraulic machine in order to accomplish some useful or desirable function.
Hydraulic power pumps are commonly connected to a hydraulic motor, hydraulic cylinder, or the like. Such hydraulic actuators are used to turn the wheels or other propulsion means of a vehicle, to lift, manipulate or otherwise position a heavy load, or for similar type purposes.
Various mechanisms are used to adjust the volume of fluid displaced per revolution of a mechanical power input shaft. Specifically, conventional displacement adjustment mechanisms used in piston pumps adjust the distance that each piston reciprocates for each revolution of a power shaft, thereby causing an adjustment in the volume of the fluid that is displaced by such a piston. Such conventional displacement adjusting mechanisms generally suffer from a high part count, difficult assembly processes, high cost, precisely machined part tolerances, poor efficiency, and other problems that are well know in the art.
Another attempted solution is seen in U.S. Pat. No. 5,190,449 to Stalter et al. The Stalter reference teaches a novel mechanism that accomplishes adjustable displacement without the need to adjust the distance that pistons reciprocate. The Stalter mechanism uses electromechanical valves to electrically or synthetically commutate the opening and closing of the inlet check valves and optionally the outlet check valves.
In the simplest embodiment of the Stalter mechanism an electromechanical inlet valve will be actuated open and closed at the appropriate phases of shaft rotation as required for each shaft revolution to determine if the fluid displacement by a piston reciprocation is displaced through an outlet valve or in a reversed direction through an inlet check valve that is adapted to be electrically held in an open position. While the Stalter mechanism holds promise for the future, to date, there have been no known commercial applications of the Stalter mechanism. To date, embodiments of the Stalter mechanism have suffered from bulky dimensions, high complexity of operation, and high cost.
Thus, it is a principal object of the present invention to provide an improved and simplified adjustable displacement hydraulic pump.
Yet another object of the present invention is to provide an adjustable displacement hydraulic power unit that operates with improved efficiency.
It is yet another object of the present invention to provide a more compact adjustable displacement hydraulic power unit.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.